In angina pectoris, the pain radiating down the left arm is mediated by increased activity in afferent (sensory) fibres contained in the
**Core Concept**
The pain in angina pectoris is a result of myocardial ischemia, which activates nociceptors in the heart. Afferent sensory fibers in the cardiac nerves transmit this pain signal to the spinal cord and brain, where it is perceived as chest pain radiating to the left arm.
**Why the Correct Answer is Right**
The correct answer involves the cardiac nerves, specifically the **vagus nerve (V)** and the **phrenic nerve**. The vagus nerve contains afferent fibers that innervate the heart, and the phrenic nerve contains afferent fibers that innervate the pericardium and diaphragm. These afferent fibers transmit pain signals from the heart and pericardium to the spinal cord and brain.
**Why Each Wrong Option is Incorrect**
* **Option A:** The **sympathetic nerves** are involved in the "fight or flight" response and are not directly involved in transmitting pain signals from the heart.
* **Option B:** The **vagus nerve (V)** is involved in the parasympathetic nervous system and is responsible for regulating heart rate, but it is not the primary nerve responsible for transmitting pain signals from the heart.
* **Option D:** The **intercostal nerves** are involved in transmitting pain signals from the chest wall, but they are not directly involved in transmitting pain signals from the heart.
**Clinical Pearl / High-Yield Fact**
The pain in angina pectoris is often described as squeezing or pressure-like, and it may radiate to the left arm, jaw, or neck. This is because the afferent fibers in the cardiac nerves transmit a complex pain signal that is perceived as a diffuse, burning sensation.
**Correct Answer:** C. The phrenic nerve.